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A multilayer aperture antenna array in millimeter-wave band is presented in this article. The antenna array is based on glide-symmetric holey gap-waveguide technology combined with E-plane insertion gaps for a low-cost and low-loss design. The radiating part of the antenna array is formed by an array of sixteen aperture antennas, grouped in four sets of 2x2 antenna subarrays in E-plane configuration. The 2x2 subarrays are fed by a one-to-four corporate feeding network in E-plane with holey gap-waveguide technology. The antenna array has been manufactured with high precision stereolithography (SLA) and subsequent metal plating. This design procedure yields a low-cost and low-weight manufacturing process for functional prototypes. The complete array has been manufactured and measured, comparing its performance with the simulation results. Measurements show an input reflection coefficient below -10 dB which ranges from 68 GHz to 74 GHz. The measured radiation patterns suit adequately the defined ones in the design stage. Moreover, gain above 19 dBi in the entire operating frequency band is achieved with a 74.1% mean antenna efficiency.

Energy efficiency is a major issue in the fifth generation (5G) of cellular networks as they require an ultra-dense deployment of small base stations (SBSs) to meet the forecasted traffic demands. Switching off cells is a widely recognized strategy to reduce the power consumption of these networks during off-peak conditions but, as times goes by, these demands change, thus requiring the activation or deactivation of a different set of cells that provide the users with a minimum QoS. In this context, the optimization problem of selecting which cells have to be switched on/off in each period of time has been approached from the dynamic multi-objective evolutionary (MOEA) domain, by proposing a novel restart method that enables the algorithms to react to changes in the traffic demands. The newly devised operator, named Adjacent Cell Restart (ACR), is based on exploiting the spatial continuity of the mobile users in the network. The experiments over a set of 9 ultra-dense networks with increasing densities of both users and base station has shown the enhanced capabilities of the ACR-enabled dynamic MOEAs to better approximate the newly induced the Pareto fronts in consecutive periods of time.

Mobile communications are growing and the number of users is constantly increasing at an accelerated rate, as well as the demand for the services they request. In the last few years, many efforts have focused on the design and deployment of the new fifth generation (5G) cellular networks. However, novel highly demanding applications, which are already emerging, need to go beyond 5G in order to meet the requirements in terms of network performance. But, at the same time, as the Earth does not allow us to increase the carbon footprint anymore, the energy consumption of the communication networks has to be critically taken into consideration. A multi-objective approach for addressing all these issues is therefore required. This work develops a cellular network framework that allows the evaluation of different system parameters over dynamic traffic patterns, as well as optimizing the different conflicting objectives simultaneously. The novelty relies on that the optimization process integrates key performance indicators from different layers of the network, namely the radio and the network layers, aiming at reaching solutions that account for the power consumption of the base stations, the total capacity provided to mobile users and also the signaling cost generated by handovers. Moreover, new metrics are needed to evaluate different solutions. Starting from the well-known energy efficiency merit factor (bits/Joule), three new merit factors are proposed to classify the network performance since they take into account several network parameters at the same time. These indicators show us the ideal working point that can be used to plan the point of operation of the network. These operation points are a medium-high power and capacity load and a low signaling load.

The upcoming high-speed wireless communication systems will be hosted by millimeter and sub-millimeter-wave frequency bands. At these frequencies, electromagnetic waves suffer from severe propagation losses and non-line-of-sight (NLOS) scenarios. A new wireless communication paradigm has arrived to resolve this situation through the use of reconfigurable intelligent surfaces (RIS). These metadevices are designed to reconfigure the wireless environment in a smart way. Traditional RIS designs based on the implementation of 2-D configurations have been considered up to now. However, 3-D structures enable an extra degree of freedom in the design that can be taken as an advantage for the development of improved RIS structures with advanced functionalities. This article proposes the implementation of a novel electronically-reconfigurable RIS based on the use of 3-D graphene meta-atoms. The reconfigurability lies on the graphene conductivity, easily tunable with a biasing voltage. Different conductivity values vary the meta-atom electromagnetic response, modifying the RIS functionality. A multi-objective optimization framework determines the optimal phase state of each meta-atom to accomplish the desired RIS performance. The operation of the RIS as an efficient beam steerer/splitter, absorber and polarization selector is validated with full-wave results.

A reconfigurable phase shifter in waveguide composed by glide-symmetric holey unit cells is presented in this paper. The hole depths of this kind of holey unit cell are modified to allow a phase shift variation in the waveguide. The adjustment of the hole depths in the unit cell is achieved by the insertion of screws in the holes that are implemented as through holes. This advantage in implementation of reconfigurable elements inside the holes is added to the low-dispersive behaviour of the holey glide-symmetric unit cells. Both features make possible the design of a reconfigurable phase shifter in waveguide with flat phase shift responses. The phase shifter design proposed in this work provides a maximum phase shift of 90° with good impedance matching from 50 GHz to 75 GHz.

This paper presents the applicability of using the time-gating technique to propagation measurements in order to recreate new scenarios. This technique, which has been studied previously in antenna measurements, is applied in propagation measurements to modify and tune the reflections that a particular propagation scenario exhibits. A new configuration for shielded chambers is proposed, where half of the chamber is covered with absorbers (anechoic chamber) and half without absorbers (reverberation chamber). This configuration and the time-gating technique allow the study of the propagation environment for the new recreated scenarios.

This paper analyzes thoroughly the dispersion and filtering features of periodic holey waveguides in the millimeter-wave frequency range. Two structures are mainly studied depending on the glide and mirror symmetries of the holes. A parametric study of the dispersion characteristics of their unit cells is carried out. Glide-symmetric holey waveguides provide a higher propagation constant and a low dispersion over a wide frequency range regarding hollow waveguides. This property is particularly useful for the design of low-loss and low-dispersive phase shifters. We also demonstrate that glide-symmetric holey waveguides are less dispersive than waveguides loaded with glide-symmetric pins. Furthermore, we perform a Bloch analysis to compute the attenuation constants in holey waveguides with mirror and broken glide symmetries. Both configurations are demonstrated to be suitable for filter design. Finally, the simulation results are validated with two prototypes in gap-waveguide technology. The first one is a 180$^{o}$ phase shifter based on a glide-symmetric holey configuration that achieves a flat phase shift response over a wide frequency range (27.5\% frequency bandwidth). The second one is a filter based on a mirror-symmetric holey structure with 20-dB rejection from 63 GHz to 75 GHz.

ACKNOWLEDGMENT The authors would like to thank the Fraunhofer-Heinrich- Hertz-Institut for acquiring and sharing the data associated to the rooftop and auditorium communication scenarios, the NextG Channel Model Alliance for creating a space to share public databases of propagation measurements, José Francisco Cortés-Gómez for the graphical support, Carmelo García-García for his help in the measurements acquisition, and Sohrab Vafa, Pablo Padilla and Francisco Luna-Valero for their valuable comments., This article presents a novel application of the t-distributed Stochastic Neighbor Embedding (t-SNE) clustering algorithm to the telecommunication field. t-SNE is a dimensionality reduction algorithm that allows the visualization of large dataset into a 2D plot. We present the applicability of this algorithm in a communication channel dataset formed by several scenarios (anechoic, reverberation, indoor and outdoor), and by using six channel features. Applying this artificial intelligence (AI) technique, we are able to separate different environments into several clusters allowing a clear visualization of the scenarios. Throughout the article, it is proved that t-SNE has the ability to cluster into several subclasses, obtaining internal classifications within the scenarios themselves. t-SNE comparison with different dimensionality reduction techniques (PCA, Isomap) is also provided throughout the paper. Furthermore, post-processing techniques are used to modify communication scenarios, recreating a real communication scenario from measurements acquired in an anechoic chamber. The dimensionality reduction and classification by using t-SNE and Variational AutoEncoders show good performance distinguishing between the recreation and the real communication scenario. The combination of these two techniques opens up the possibility for new scenario recreations for future mobile communications. This work shows the potential of AI as a powerful tool for clustering, classification and generation of new 5G propagation scenarios., Spanish Program of Research, Development, and Innovation under Project RTI2018-102002-A-I00, Junta de Andalucía under Project B-TIC-402-UGR18 and Project P18.RT.4830, Ministerio de Universidades, Gobierno de España under Predoctoral Grant FPU19/01251

This work was supported in part by the Spanish Research and Development National Program under Project TIN2016-75097P and Project RTI2018-102002-A-I00, in part by "Junta de Andalucia" under Project B-TIC-402-UGR18 and Project P18.RT.4830, and in part by the Predoctoral Grant FPU18/01965., In this brief, we present a low-loss mechanically reconfigurable phase shifter implemented in gap-waveguide technology for mm-wave frequencies. The proposed design gives a practical implementation of tuning elements inside the waveguide providing alternatives to the use of the E-plane split waveguide at high frequencies in order to avoid leakage losses. The depicted phase shifter design is based on a H-plane split waveguide. The phase shift is controlled by means of a tuning screw, which exerts pressure on a flexible metallic strip inserted inside the waveguide. The flexible strip bends with different curvature radii and determines the phase shift at the output port. Cost-effective manufacturing and simple implementation of the flexible metallic strip are achieved by means of the gap-waveguide design. A prototype has been manufactured for validation purposes. Good impedance matching is achieved from 64 GHz to 75 GHz providing a 15.8% impedance bandwidth. The results show a maximum phase shift of 250° with a maximum and mean insertion loss (IL) of 3 dB and 1.7 dB, respectively., Spanish Research and Development National Program TIN2016-75097P RTI2018-102002-A-I00, Junta de Andalucia B-TIC-402-UGR18 P18.RT.4830, FPU18/01965

This paper presents a compact and low-loss V-band waveguide phase shifter based on glidesymmetric pin configuration. This kind of higher symmetry permits the control and improvement of the electromagnetic behavior or radiofrequency devices, as it is the case of the proposed phase shifter. The study of the dispersion diagram of the phase shifter unitary cell demonstrates that the pin configuration is a proper option for introducing a phase shift in a waveguide-based system. There is a significant increase in terms of phase shift when using a glide-symmetric pin distribution compared to its corresponding nonglide- symmetric configuration. Through this paper, the key geometrical parameters are also determined. The complete phase shifter is composed of an optimized cascade of tailored unitary cells so that the desired final phase shift value is achieved. A prototype has been manufactured in order to validate the theoretical approach through the comparison of phased shifters with both non-glide-symmetric and glide-symmetric configurations. The measurement results demonstrate the higher performance and compactness of the glidesymmetric phase shifter. For the same distance, the glide-symmetric version of the phase shifter provides more than 60% of phase shifting compared to the non-glide-symmetric phase shifter. Both phase shifters have a good impedance matching between 46 and 60 GHz and an insertion loss lower than 1 dB, thus clearly enabled as a 5G technology., This work was supported in part by the Spanish Research and Development National Program and FEDER under project TIN2016-75097-P, in part by the Universidad de Málaga, under Grant PPIT.UMA.B1.2017/15, in part by the Universidad de Granada under Project PPJI2017.15, and in part by the Universidad de Granada through the grant program ``Becas de iniciación a la investigación'' from the Plan Propio de Investigación.

This paper presents the compact design of a substrate-integrated waveguide (SIW) antenna based on H-plane aperture structure. The antenna is composed by a coaxial feeding and an aperture. In this aperture inner metallic vias are introduced acting as partially detached walls in order to form 4 adjacent subapertures at the end of the aperture antenna. Thus, the field from the feeding is divided in different wavefronts that are composed at the antenna aperture to get an endfire radiation. In this manner, a flatter wavefront is generated to achieve high directivity. Additionally, some periodic parallel strips are printed after antenna aperture to improve the impedance matching with the air. The proposed antenna has impedance matching below -10 dB from 34 to 36 GHz with nearly constant gain between 13 and 15 dBi. A prototype is manufactured to validate the proposed antenna design.

This paper presents the applicability of using structures to control the phase shift in a waveguide phase shifter. By means of dispersion diagrams, different phase shift unit cells are analyzed. Glide symmetry is also applied to some of these unit cells to evaluate its effects in the propagating modes. Then, unit cells with best dispersive behaviour are selected to design two waveguide phase shifters, one by pinned unit cells and the other by holey pinned unit cells. Both waveguide phase shifters are well matched in the frequency range from 50-75 GHz with insertion losses lower than 0.5 dB. The phase shift produced by both waveguide phase shifter is also evaluated. Pinned waveguide phase shifter is more dispersive compared to the holey waveguide phase shifter, producing a phase shift deviation over 180° of ±50° and ±10°, respectively.

Smart Communities demand a huge amount of data to monitor different human activities. Until now, wireless sensor networks (WSNs) have provided these data with a low cost and low intelligence networks. However, the constraints and the required baseline performance of WSNs have increased exponentially, and there is a lack of a global proposal to satisfy the demand of Smart Communities. There are several approaches regarding efficient WSN deployments to maximize network lifetime and performance. The vast majority of those proposals try to separately address several inherent constraints and limitations related to energy and node lifetime. In fact, they typically provide efficient management approaches based on existing solutions, but they do not propose new tools or algorithms to afford them. To tackle this problem in a global manner, we introduce the concept of intelligent WSNs. In order to outfit the WSN with a huge amount of possibilities to route and control the different nodes, our nodes incorporate the possibility of transmitting and receiving signals from/to several nodes jointly through beamforming. In our approach, this latter technique is intelligently applied to allow the deployment of new WSNs to be able to react and to adapt its features depending on the environmental conditions, maintaining QoS and enlarging network lifetime. This is the main goal of our proposal.

This work presents an embedded printed antenna with omnidirectional azimuth coverage for automotive applications. A cavity-backed circular patch antenna (CBCPA) is designed to operate as an omnidirectional azimuth coverage, vertically polarized antenna at 2.4 GHz. We introduce the CBCPA design for car wireless communication applications. The CBCPA is embedded in the car roof to reduce any aerodynamic effect, using the rooftop as a ground plane for the proper monopolar radiation pattern generation. This design maintains the performance of the antenna, avoiding back radiation inside the car due to the metallic cavity and metallic rooftop. The design offers a high-efficiency homogeneous pattern in the azimuth. The use of low-profile and lightweight materials into a single cavity-backed configuration is also an advantage of this design that makes it suitable for integration in car platforms. Additionally, the cost of the antenna is reduced compared to other antenna options. This design represents a useful application to monopolar radiation patterns in microstrip technology. In our study, the CBCPA is mounted on a vehicular platform by simulation to validate the antenna characteristics.

Electromagnetic shielding of metallic enclosures with an aperture are simulated and measured in the frequency and time domain in this paper. Recently, several new figures of shielding effectiveness (SE) in the time domain have been proposed. Much work has been done regarding numerical simulations; however, little work related to measurements has been carried out. In this paper, we obtain the simulated and measured results for these SE definitions when an incident plane wave, with a determined bandwidth, excites the enclosure. The plane wave can be treated as a reference interference to compare with other cases. Measurements and simulations are in good agreement. This study evaluates the new definitions and compares them with the classical definition in the frequency domain. The effect of the probes, a dipole or a loop, has also been analyzed. Finally, the SE values are obtained for a sweep of the size of the aperture providing a unique value of equivalent SE for the most critical parameter and for a determined bandwidth, and allowing direct comparison with other enclosures.

An embedded folded, printed, quadrifilar helix antenna (FPQHA) with a wide-angle coverage for unmanned aerial vehicles (UAVs) telemetry and remote control systems is presented in this article. The novelty of this design is that the FPQHA needs to be designed carefully due to UAV tail dimensions and weight constraints while maintaining a high performance to be integrated in the inner part of the UAV tail fuselage to reduce aerodynamic drag. The radiating terminal, formed by a folded, printed, four-helix, radiating section and a compact feeding network, is designed to provide left-handed, circular polarization (LHCP). The complete design offers a very homogeneous pattern in azimuth with a very good axial-ratio (AR) level over a wide range of elevation angles. The use of low-loss and lightweight materials is also an advantage of this design. The wide radiation pattern favors its use for multielement communication systems. Finally, the antenna performance results are obtained mounted inside a UAV tail platform.

The expected advent of the Internet of Things (IoT) has triggered a large demand of embedded devices, which envisions the autonomous interaction of sensors and actuators while offering all sort of smart services. However, these IoT devices are limited in computation, storage, and network capacity, which makes them easy to hack and compromise. To achieve secure development of IoT, it is necessary to engineer scalable security solutions optimized for the IoT ecosystem. To this end, Software Defined Networking (SDN) is a promising paradigm that serves as a pillar in the fifth generation of mobile systems (5G) that could help to detect and mitigate Denial of Service (DoS) and Distributed DoS (DDoS) threats. In this work, we propose to experimentally evaluate an entropy-based solution to detect and mitigate DoS and DDoS attacks in IoT scenarios using a stateful SDN data plane. The obtained results demonstrate for the first time the effectiveness of this technique targeting real IoT data traffic., This research was funded by EU, European Regional Development Fund, and the regional government of Extremadura, Spain, grant number IB18003, the Spanish Ministry of Science, Innovation and Universities grant numbers TIN2016-75097-P, RTI2018-102002-A-I00, PEJ2018-003648-A and FEDER and Junta de Andalucía grant number B-TIC-402-UGR18.

This work has been supported by the the Spanish and Andalusian goverments, and FEDER, under contrats TIN2016-75097-P, RTI2018-102002-AI00 and B-TIC-402-UGR18. Francisco Luna also acknowledges support from Universidad de M ' alaga. The authors thankfully acknowledges the support provided by the Supercomputing and Bioinformatics center of the University of Malaga., Network densification with deployments of many small base stations (SBSs) is a key enabler technology for the fifth generation (5G) cellular networks, and it is also clearly in conflict with one of the target design requirements of 5G systems: a 90% reduction of the power consumption. In order to address this issue, switching off a number of SBSs in periods of low traffic demand has been standardized as an recognized strategy to save energy. But this poses a challenging NP-complete optimization problem to the system designers, which do also have to provide the users with maxima capacity. This is a multi-objective optimization problem that has been tackled with multi-objective evolutionary algorithms (MOEAs). In particular, a problem-specific search operator with problem-domain information has been devised so as to engineer hybrid MOEAs. It is based on promoting solutions that activate SBSs which may serve users with higher data rates, while also deactivating those not serving any user at all. That is, it tries to improve the two problem objectives simultaneously. The resulting hybrid algorithms have shown to reach better approximations to the Pareto fronts than the canonical algorithms over a set of nine scenarios with increasing diversity in SBSs and users., Spanish goverment, Andalusian goverment, European Commission TIN2016-75097-P RTI2018-102002-AI00 B-TIC-402-UGR18, Universidad de Malaga, Supercomputing and Bioinformatics center of the University of Malaga

This communication presents the design of a two-port electronically tunable phase shifter at K band. The phase shifter consists of a 3 dB hybrid coupler loaded with reflective phase-controllable circuits. The reflective circuits are formed by varactors and non-sequential impedance transformers which increase the operational bandwidth and the provided phase shift. The final phase shifter design is formed by two loaded-coupler stages of phase shifting to guarantee a complete phase turn. An 18 GHz phase shifter design with dynamic range of 600 degrees of phase shift is depicted in this document. The prototype is manufactured and validated through measurements showing good agreement with the simulation results., This work has been partially supported by the TIN2016-75097-P, RTI2018-102002-A-I00, and EQC2018- 004988-P projects of the Spanish National Program of Research, Development, and Innovation and project B-TIC-402-UGR18 of Junta de Andalucía

The expected advent of the Internet of Things (IoT) has triggered a large demand of embedded devices, which envisions the autonomous interaction of these sensors and actuators while offering all sort of smart services. However, these IoT devices are limited in compute, storage, and network capacity which makes them easy to hack and compromise. To achieve a safe development of IoT, it is necessary to develop scalable security solutions optimized for the IoT ecosystem. To this end, Software Defined Networks (SDN) is a promising paradigm proposed in 5G that could help to detect and mitigate Denial of Service (DoS) attacks. In this article, we propose an experimental evaluation of an entropy-based solution to detect and mitigate DoS attacks in different scenarios. Results show the effectiveness of this mechanism. The proposed test beds have been conducted by using real data flows, in order to validate the solution under authentic IoT traffic.

This document presents the design of an array of helix antennas in axial mode based on higher symmetries. These higher symmetries permit, for a given frequency, the miniaturization of the antenna. Therefore, an array formed by this kind of miniaturized antennas presents lower mutual coupling among the constituting antennas. A comparison is made between the performance of antenna arrays formed by conventional and glide-and-twist-symmetrical helix antennas. The results show a decrease in mutual coupling in the glide-and-twist-symmetrical helix array, regarding to the conventional helix array, for the same element spacing. Moreover, better radiation performance is achieved in terms of directivity and gain in the miniaturized helix array.

Ultra-dense networks (UDNs) are recognized as one of the key enabling technologies of the fifth generation (5G) networks, as they allow for an efficient spatial reuse of the spectrum, which is required to meet the traffic demands foreseen for the next coming years. However, the power consumption of UDNs, with potentially hundreds of small base stations (SBSs) within each macrocell, is a major concern for the cellular operators, and has to be properly addressed prior to the actual deployment of these 5G networks. Among the different existing approaches to address this issue, a widely accepted strategy lies in the selective deactivation of SBSs, but without compromising the QoS provided to the User Equipments (UEs). This is known as the Cell Switch-Off (CSO) problem. The typical formulation of this problem is based on estimations of the traffic demand of the User Equipments (UEs) within the network. But these estimations could not be met. This work approaches these uncertain scenarios by extending the CSO problem with additional objectives that account for the robustness of the solutions to disturbances in these traffic estimates. To do so, a computationally demanding Monte-Carlo sampling is used to evaluate each solution. To manage such an increasingly large computing cost, a parallel version of the NSGA-II algorithm that is able to run on a computing platform composed of more than 500 cores has been used. It is able to compute in roughly 2 hours, an accumulated execution time of more than 42 days, which is within the expected timeframe of operators to make changes in the network configuration.

Here we propose the use of twist and glide symmetries to increase the equivalent refractive index in a helical guiding structure. Twist- and glide-symmetrical distributions are created with corrugations placed at both sides of a helical strip. Combined twist-and glide-symmetrical helical unit cells are studied in terms of their constituent parameters. The increase of the propagation constant is mainly controlled by the length of the corrugations. In our proposed helix antenna, twist and glide symmetry cells are used to reduce significantly the operational frequency compared with conventional helix antenna. Equivalently, for a given frequency of operation, the dimensions of helix are reduced with the use of higher symmetries. The theoretical results obtained for our proposed helical structure based on higher symmetries show a reduction of 42.2% in the antenna size maintaining a similar antenna performance when compared to conventional helix antennas., This research was funded by the Spanish Ministerio de Ciencia, Innovación y Universidades with European Union FEDER funds, grant number TIN2016-75097-P, and by Universidad de Granada, under the project PPJI2017.15. Also, this work has been partially supported by the Universidad de Granada through the grant program “Becas de iniciación a la investigación” from Plan Propio de Investigación.

This piece of work aims to be a complementary document extending our previous article ‘Broadband electronically tunable reflection-based phase shifter for active-steering microwave reflectarray sys...

A former definition states that a brain-computer Interface provides a direct communication channel to the brain without the need for muscles and nerves. With the emergence of wearable and wireless brain-computer interfaces, these systems have evolved to become part of wireless body area networks, offering people-centric applications such as cognitive workload assessment and detection of selective attention. Currently, wireless body area networks are mostly integrated by low-cost devices that, because of their limited hardware resources, cannot generate secure random numbers for encryption. This is a critical issue in the context of new Internet of Things device communication and its security. Such devices require securing their communication, mostly by means of the automatic renewal of the cryptographic keys. In the domain of the people-centric Internet of Things, we propose to use wireless brain-computer interfaces as a secure source of entropy, based on neuro- activity, capable to generate secure keys that outperforms other generation methods. In our approach, current wireless brain-computer interface technology is an attractive option to offer novel services emerged from novel necessities in the context of the people-centric Internet of Things. Our proposal is an implementation of the human-in-the-loop paradigm, in which devices and humans indistinctly request and offer services to each other for mutual benefit.

This paper is a study of the inhomogeneity reduction for near-field acquisition in high-resolution magnetic resonance imaging (MRI) systems. The acquisition homogeneity in MRI imaging modality is an open issue concerning the optimal MRI image generation in terms of the RF signal acquisition. The acquisition inhomogeneity is related to the radiation patterns of the receiving antennas and its location in the MRI system, among other relevant aspects. The acquisition inhomogeneity is translated into two main effects: pattern ripples at the outer cylindrical rings and radial inhomogeneity when comparing the center value (maximum) with the rest of the pattern. To overcome these effects, two strategies are proposed. In the first one, it is proposed to progressively vary the antenna location in the azimuthal array distribution. In the second one, it is proposed to progressively vary the antenna amplitude and phase feeding in the array distribution. To compute a figure of merit of the pattern radial uniformity and the ripples, two metrics are defined in this paper. It is proved that both the progressive modification in the location at each array ring and the variation of the feeding phase of each array ring reduce the pattern ripples and radial inhomogeneity. Optimal values for either the angular rotation or the feeding phase values can be calculated, depending on the particular dimensions of the cylinder that conforms the region of interest.

This study presents a lightweight planar patch-array reflectarray at Ku-band for satellite communications. The reflectarray is composed of two separate planar structures: the radiating interface formed by a planar multi-layered broadband patch array, and a phase shifting device formed by 3 dB/90° couplers. The radiating element is a multi-layered patch structure, designed to provide circular polarisation (CP). Each array cell phase is controlled by open-ended shifting lines of variable length connected to the 3 dB/90° couplers. The use of this kind of couplers maintains the same CP received/transmitted: the design imposes that if a right-hand CP (RHCP) [or left-hand CP (LHCP)] is received coming from the feeder, the same RHCP (or LHCP) configuration is re-radiated by the reflectarray. Additionally, the feeding horn can be moved in the x or y axes, so that the feeder angular position let re-define the radiation pattern and its pointing direction. Finally, measurements of a lightweight portable planar reflectarray prototype are provided and very good agreement is observed when compared with theoretical results.

Improving energy efficiency is one of the most important aspects in the Wireless Sensor Networks, being one of their main design goals. A key technique used in a wide range of wireless technologies is beamforming, as it provides a way of efficiently transmitting the radio signals towards a given (set of) target direction(s). In this work, the beamforming technique is jointly used with clustering in order to increase the lifetime in WSNs. In particular, scenarios with 2, 4, 5 and 10 nodes that install either ideal isotropic antennas or conventional dipoles are considered. The target direction to configure the beam has been set to ϕ = 0° and ϕ = 45°. Also, it is shown that beamforming can be used to transmit both efficiently and securely the signals by decreasing the power radiated in the direction of an enemy node. Different cases are analyzed with a different number of base stations and a different number of enemy nodes. A genetic algorithm (GA) is applied to optimize the number of clusters and the phase and amplitude of the antennas of the WSN nodes in all scenarios and cases raised. Up to the authors’ knowledge, beamforming techniques have not been previously applied together to reduce the energy consumption in WSN and secure the communications simultaneously.

This document provides the complete design of a broadband planar multilayered reflectarray based on circular stacked patches and reflective printed lines. These devices are conceived for their use in satellite communications at microwave and millimeter frequencies. The working principle of the reflectarray is based on the reception and front wave correction by means of printed phase shifters embedded in a phased array structure. Our approach is based on an array of circular stacked patches connected to reflective line shifters. Each reflective shifter at each array cell introduces a phase variation that can be modified due to the line length. The work implies the selection and design of the unitary radiating element and reflective lines of the array, along with the complete reflectarray definition and building up based on this constituting array cell. This work provides the initial specifications and constraints, a complete design, and a manufactured prototype with its performance results.

In recent works, it is demonstrated that, depending on the different spatial distributions and distance between elements, there exists a different true polarization diversity (TPD) configuration that provides a high improvement in terms of capacity. This means that it is necessary to choose the appropriate TPD configuration to maximize the multiple-input-multiple-output (MIMO) capacity. In this work, a genetic algorithm is used to optimize the element positions for four new different configurations in combination with the TPD technique. It is shown that, for some configurations, the same polarization option is always found to reach the maximum capacity. Based on this, some novel design rules are provided to maximize MIMO capacity when the area for placing the antennas is very small. This is the case for most of the wireless devices, where the antenna design and location is one of the latest design constraints to be taken into consideration in the device design.

Distributed beamforming in a wireless sensor network (WSN) allows the sensor nodes to reduce the energy required to perform wireless communications, a critical issue to prolong the lifetime of this kind of systems, in which the node energy is supplied by limited sources such as batteries. This works analyzes the effect of the dimensionality in the problem instances to accomplish an efficient distributed beamforming, taking into account two separate factors: the number of sensor nodes involved in the beamforming and the type of antenna these nodes have installed. By using both classic and state-of-the-art metaheuristics, a thorough set of experiments have been performed, showing that, given the antenna type, the number of nodes makes the beamforming problem become harder because of the required synchronism. The results have also shown that beamforming is an effective technique to increase the WSN lifetime.

This paper presents an analytical expression that models the tilt angle of directors in a nematic liquid crystal (LC), depending on its elastic properties, its dielectric anisotropy, and the quasi-static electric field applied. The analytical solution obtained is fast and easily computable in comparison with numerical estimations and is of special interest in radiofrequency; for instance, for the LC modeling in full-wave electromagnetic simulators in the design process of electronically tunable devices, such as microwave phase shifters or electronically steerable antennas for satellite communications. Subsequently, a comparison is made between numerical approaches (self-implemented shooting method) and the analytical formulas when varying the parameters of the LC, being demonstrated its usefulness. The average LC director is then obtained and used to form the full permittivity tensor that completely characterizes the electrical properties of the material. Finally, an electromagnetic simulation is carried out to show the capabilities of the LC as a tunable phase shifter. It is shown that only 5 cm of a commercial 200-mm LC mixture is necessary to achieve 360 of the maximum variable phase shift at the 30-GHz band, This work was supported in part by the Spanish Research and Development National Program under Project TIN2016-75097-P, and in part by the Ministerio de Economía under Project TEC2017-85529-C3-1-R.

© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. The power consumption foreseen for 5G networks is expected to be substantially greater than that of 4G systems, mainly because of the ultra-dense deployments required to meet the upcoming traffic demands. This paper deals with a multi- objective formulation of the Cell Switch-Off (CSO) problem, a well-known and effective approach to save energy in such dense scenarios, which is addressed with an accurate, yet rather unknown multi-objective metaheuristic called MOCell (multi- objective cellular genetic algorithm). It has been evaluated over a different set of networks of increasing densification levels. The results have shown that MOCell is able to reach major energy savings when compared to a widely used multi-objective algorithm. TIN2016-75097-P Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech.

The paradigm shift that has to take place in the new 5G networks in order to meet the expected data rates is a huge technological challenge. The use of super dense heterogeneous networks is one of the most promising alternatives to provide services with speeds above 1 Gbps. Another option to increase bandwidth is to engineer base stations at higher working frequencies and, thus higher available bandwidth, but also having the issues of the component cost and the increased propagation losses. This work evaluates the deployment of ultradense networks with base stations at different frequencies, ranging from 2 GHz to 60 GHz. Different scenarios that use several densities of both base stations and user equipments have been analyzed. The network performance has been measured in terms of Capacity, Signal to Interference plus Noise Ratio, and Energy Consumption.

Wireless Communication technologies are in continuous evolution. Around the world, many Universities try to provide innovative laboratory courses to train their students in this field. In this paper, a ubiquitous laboratory course for wireless communications is described. The laboratory course has been designed so that the students have to complete six different experiments. Three of these experiments have been designed to use advanced professional network testing tools in order to provide practical experience in simulation tools. Two additional experiments have been implemented in order to provide hands-on measurements through the student's mobile device. This is a novelty and provides the students with an example of ubiquitous learning. Finally, in the last experiment, the students manufacture a WiFi antenna. The laboratory has been designed so that the students develop different practical skills in each experiment. This laboratory course facilitates applied learning and the consolidation of theoretical concepts.

This paper presents a fair comparison between different representative link layer protocols for wireless sensor networks: S-MAC, DRAND and Z-MAC protocols. The performance of these protocols is evaluated in terms of power consumption, the use of the propagation channel resources and the traffic rate provided for each node and the overall aggregated traffic. For the experimentation and the performance analysis, an evaluation scenario is built up, including a set of nodes randomly placed around reference places. This scenario is evaluated under different circumstances and traffic load levels. In addition, some conflictive issues are included, such as the presence of `bottle necks' or egoist nodes in the network, and their influence is analyzed for each protocol in order to determine which one copes better with hostile conditions.

This paper presents a new course, Radionavigation Systems, whose laboratory and theoretical components complement each other to enhance student learning. Radionavigation skills and knowledge are taught by means of various instructional methods, and the laboratory successfully merges hands-on learning using specific instrumentation and software simulation tools, with m-learning and a competition. The relationship between cognitive and psychomotor learning outcomes is discussed. These instructional methods proved highly motivating to students. Oral presentations and report preparation skills also improved in students who completed the course. The experiments designed for the course are discussed in the light of student surveys, student grades, and the work carried out by the lecturer. The evaluation results demonstrate a high degree of success in meeting the initial goals of the course. The main drawback of the current course is related to equipment availability. Student motivation was high throughout the course. The course as designed is transferable to other universities.

Cooperative or distributed multiple-input multiple-output (MIMO) systems are promising techniques for achieving large performance gains in wireless networks. Recently, a novel method for measuring these systems on a reverberation chamber has been proposed. In this letter, this technique is used to measure different cooperative massive MIMO (CM-MIMO) systems. The correlations of these systems have been shown, and capacities under different conditions are provided for different CM-MIMO systems. In addition, the behavior of these systems with Rician fading is also analyzed. These results show the impact of these new propagations channels on the fifth-generation mobile communication systems, which will be basic for the development of such systems.

In this letter, we demonstrate that the dispersion properties of printed double-sided parallel-strip lines can be controlled by using glide symmetry. Glide symmetry is introduced in with corrugations in both strips of a double-sided line. We demonstrate that glide symmetry eliminates the stopband between first and second propagating modes and yields to a higher propagation constant, preserving its linearity, and the broadband nature of the underlying guiding technology. Thus, the glide-symmetric double-sided line can be designed to possess a high equivalent refractive index in an ultrawide range of frequencies. These exceptional properties have been numerically and experimentally validated. Finally, we demonstrate the possibilities of this technology with a specific design, a glide-symmetric double-sided parallel-strip line with filtering properties. Potential applications are low-dispersive leaky-wave antennas and electromechanical tunable phase shifters and filters.

The home care crew scheduling (HCCS) problem is a planning task whose goal is to allocate a set of professional caregivers in the most efficient way to perform a number of assistencial and health care visits to the customers private homes. This is part of an important trend in advanced health care systems, to promote "independent living" specially in situations of dependency on long-term care. This not only ensures a higher quality of life but also a lower cost for society. Real instances of the HCCS problem are large and highly constrained due to both caregivers' contract limitations and customers' needs. This paper presents an advanced parallel model that solves HCCS problems using a grid-based asynchronous evolutionary algorithm (EA). Our approach has been tested using a grid computing facility of up to 300 nodes. The algorithm is a modified (1 + lambda) EA, parallelized using a master/worker model that minimizes communication requirements and processor bottlenecks by distributing both the execution of the EA operators and the evaluation of solutions. We have used three large real-world instances provided by a private company to perform experimentation with different configurations of the EA and number of workers. Results show that our algorithm achieves solutions that clearly outperform the solution provided by the company and the grid-based algorithm is able to handle real world HCCS problems The work of Francisco Luna and Juan F. Valenzuela is funded by the Spanish Ministry of Economy, Industry and Competitiveness under contract TIN2016-75097-P. The work of Alejandro Cervantes and Pedro Isasi is funded by the Spanish Ministry of Science and Innovation under contract TIN2011-28336.